Coaching guru Nick Bollettieri believes Martina Hingis could struggle on her return to the tennis tour after a three-year absence.
The Swiss former world number one, who retired in 2002 after nagging foot and ankle problems, makes her comeback at the Gold Coast event next week and has been handed an entry into the Australian Open.
Bollettieri, who briefly coached Hingis in 1998, believes the game has moved on while she has been away.
"I've sent her an email to wish her luck but she needs more than luck," the American told the BBC.
"The game is much stronger now than when she left. We're not just talking about eight or 10 good players out there. If you go down to 15, 20, even 50 in the world, you have a lot of very good players.
"There will be a lot of eyes on Martina and it's not going to be an easy road," added Bollettieri, who also nurtured Andre Agassi, Maria Sharapova and Monica Seles.
The Slovakia-born 25-year-old, who claimed five Grand Slam titles including three in Australia, knows she faces a big challenge if she is to survive on the women's circuit.
"If I want to play the tennis I played three years ago I would not survive," she told reporters on Queensland's Gold Coast on Friday. "I know that. You have to grow with the game and you have to get better physically and tennis-wise.
"I've been trying to work on my whole game, baseline and serve. You have to have a serve to be able to survive today and we'll see if I can bring it on, like the saying says."
After playing in the Gold Coast event Hingis will continue her comeback in Sydney the week after. The Australian Open starts on January 16.